1. Technical Field
The present invention relates to a gas generator for an air bag that protects a driver or a passenger from an impact, and more particularly to a hybrid-type gas generator that seals pressurized gas therein.
2. Description of the Prior Art
For the purpose of protecting a driver or passenger from an impact, a vehicle is equipped with an air bag device. The air bag device includes a sensor, a control unit, gas generator, an air bag, etc. The gas generator includes ignition means and gas generating means.
Upon detection of an impact by the sensor, a detection signal is supplied to a control unit, which conducts arithmetic calculation in response to the detection signal. The control unit sends an output signal representative of the result of the arithmetic calculation to the ignition means. The ignition means is thus operated. By this operation, a gas is generated abruptly and provided into the air bag (bag body). As a result, the air bag is inflated and forms a cushion that absorbs an impact between a solid structure of the vehicle and the driver or the passenger.
Although there are numerous combinations of vehicle speed and seating posture of passengers at the time of a collision, most of the current air bag devices merely deploy the bag by generating the gas all at once upon receiving a signal from a shock sensor. Therefore, an excessive force, due to the deployment of the bag, may be applied to the passengers. There are number of inventions, in which, for example, reduces such a force from being applied to the passengers when the passengers are not seated in a proper posture.
In Japanese laid-open application No. 49-33320, a plurality of igniters are activated by a low-speed shock sensor and a high-speed shock sensor, respectively, such that the force of deployment of the bag can be selected in accordance with the shock due to the collision of the vehicle.
By this method, however, although the deployment force of the bag can be selected in accordance with the extent of the shock applied to the vehicle, the deployment of the bag cannot be selected in accordance with the seating posture of the passengers.
Further, EP-0382552 teaches a gas generator device having a vessel with two completely independent and isolated chambers, defined by a partition wall, in which an igniter and a gas generating material are disposed, and an ignition system for the same. This conventional art teaches adjusting the forces of air bag deployment by providing a combination of sensors for detecting a shock applied to the vehicle, vehicle speed, and atmospheric temperature. The structure of this gas generator device, however, is very complicated and includes many parts. Therefore, it is very difficult to manufacture and to maintain reliability.
In the air bag device, it is desirable that when the degree of an impact, which is given to the driver/passenger, is small, the inflating (deploying) rate of the air bag is initially decreased, by which a small force is given to the driver when the driver is not in the regular seating position, and thereafter a large force is given to the driver/passenger so that the driver returns to the regular seating position, thus forming a cushion in front of the driver/passenger.
The object of the present invention is to provide, in a gas generator for an air bag system having two igniters, in which the deployment force of the bag can be adjusted or selected, a hybrid-type gas generator having a simpler structure that is easier to manufacture and to maintain high reliability as compared to the conventional gas generators. A gas generator for an air bag according to the present invention comprises a vessel having a pressurized gas accommodation chamber for accommodating a pressurized gas therein; a partition that divides the pressurized gas accommodation chamber into two sections; a through-hole, which is defined in the partition, for communicating the pressurized gas accommodation chamber sections; two ignition units having gas generating agents, respectively; and a gas release unit disposed in the pressurized gas accommodation chamber and having a rupturable gas sealing wall, wherein the two ignition units are disposed in the respective pressurized gas accommodation chamber sections one-by-one, or in any one of these pressurized gas accommodation chamber sections.
The structural characteristic of the gas generator of the present invention is that, the vessel is divided into two sections by a partition or a dividing wall, and connecting the sections by providing a through-hole (port). Further, a single igniter is disposed in each section, or two igniters are disposed in one of the two sections. The through-hole functions to equalize the pressure of the pressurized gas in the two sections. Therefore, the thorough-hole needs to have an area sufficient for the pressure of the filled gas in the sections to become equal.
The respective pressurized gas accommodation chamber sections may be different in volume from each other. Also, the respective gas generating agents of the two ignition units may be different in capacity from each other.
It is preferable that one of the pressurized gas accommodation chamber section is disposed in the center of the vessel whereas the other chamber section is disposed around the periphery of the one pressurized gas accommodation chamber section.
Also, it is preferable that the vessel is formed of a spherical body that combines two hemispherical bodies with one another, and the partition is formed of a plate body, which is held between the two hemispherical bodies, or formed of a plate body, which is disposed vertically with respect to the bottom surface of one of the hemispherical bodies.
The ignition unit may include an igniter accommodation vessel which is filled with an igniter material, a resistance heating body disposed within the igniter accommodation vessel, for heating upon receiving electricity, and a gas generating agent accommodation vessel, which surrounds the igniter accommodation vessel, for accommodating the gas generating agents therein.
In the gas generator of the present invention, two ignition units may operate simultaneously or with a time lag so that a generated gas pressure is adjusted, thereby changing the inflating (deploying) rate of the air bag.
When the degree of an impact is small, those two ignition units operate with a time lag, thereby decreasing the inflating rate of the air bag at an initial stage. As a result, a small force is applied to a driver/passenger who may not be in a regular seating posture, and a large force is thereafter applied to him so that he moves to the regular seating posture. Thus, a cushion can be formed in front of the driver.
Also, when the degree of an impact is large, those two ignition units operate simultaneously, thereby increasing the inflating rate of the air bag. As a result, the air bag is inflated rapidly, thereby forming a cushion in front of the driver.
The respective pressurized gas accommodation chamber selections may be identical with each other in volume, or alternatively the volumes of the respective accommodation chamber sections may be different from each other.
Moreover, the gas generating agents of the respective two ignition units may be identical with each other in capacity, or alternatively the amount of the gas generating agents may be different from each other.
In the case where the volumes of the pressurized gas accommodation chamber sections are different from each other, the inflating rate of the air bag can be changed at the initial stage by changing the order of the operation of the ignition units in the respective accommodation chamber sections. For example, in the case where the ignition unit in the accommodation chamber section having a larger volume is operated in advance, the inflating rate of the air bag at the initial stage is greater in comparison with the case where the ignition unit in the accommodation chamber section having a smaller volume is operated first.
The pressurized gas may be an inert gas, such as argon, nitrogen, helium, or the like. Those gases can be accommodated at a predetermined pressure, for example, 2510 to 5000 psi in the pressurized gas accommodation chamber.
As stated in the foregoing, the present invention realizes a gas generator for an air bag, in which the deployment speed of the bag can be varied. Namely, in the gas generator of the present invention (the pressurized chamber), containing pressurized gas therein, is divided into two sections by a partition, and the two sections are connected by the through-hole. Further, by providing two ignition units, the initial inflating (deploying) speed of the air bag is reduced to move the driver/passenger to a proper seating posture when the driver/passenger is not seated in the proper seating posture, and then applying a greater force to the passenger/driver and provide a cushion in front of the passenger. When the shock due to the collision is relatively large, the air bag is inflated at a greater speed, to inflate the air bag more quickly, to provide the cushion in front of the passenger to protect the passenger.
The gas generator of the present invention has a simpler structure, less number of parts, and therefore, easier and less expensive to manufacture.